Submitted by Kathryn Martin and Marcus Archambault
“I saw three otters right near Waldie Island,” recounted Recreation, Fish and Wildlife student David Cox of his Oct. 29 encounter. “They stuck around playing for a while. They were curious about me for a moment, but then quickly carried on doing their thing and eventually swam off upriver.”
Did you know that seeing river otters in a river, lake, or wetland is a good sign that the environment is healthy? Biologists refer to them as an indicator species. That’s because these playful predators require large amounts of prey and are very sensitive to pollution which can build up in their bodies.
The North American river otter (Lontra canadensis) is one of 13 species of otter found around the globe. They are members of the weasel family, like minks, ferrets, and wolverines. River otters have waterproof fur that allows them to live in freshwater habitats of all kinds, though coastal otters can live in marine environments. They are pescetarian carnivores, eating fish and crustaceans. Their paws are adept at working shells open for a tasty snack.
The North American river otter is found in every province and territory of Canada. Prior to colonization, they were widespread across the continent, but they are now extirpated from many southern states. Their numbers are much lower now, but still have healthy populations and are not at risk of endangerment in Canada.
Indicator species
Not only are river otters apex (or top) predators in their environments, but they also have high metabolic rates which require them to consume about 15-20 per cent of their body weight each day. In order to support an otter population, the environment must also support prey species in large enough quantities for their voracious appetites.
Their high consumption rates of water-loving creatures make them ideal candidates for testing which pollutants, like heavy metals from mining or industrial pollution, are present in the water and have built up in the food chain. This is called bioaccumulation.
Otter feces and fur can be collected in the field and then tested in the lab — their scat will show what was in the water at the time of their meal, and their fur can show levels of pollutant accumulation over time.
This was demonstrated in a 2018 study by Shannon Crowley and colleagues of otters in Pinchi Lake in central B.C. near a reclaimed mercury mine.The study found elevated levels of methyl mercury (MeHg) in otter fur compared to otters in other lakes. The authors recommend “inclusion of river otters in environmental assessments pre-, during -, and post-industrial activities.”
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Spotting otters
While you may be lucky enough to catch a glimpse of these charismatic creatures, it’s easier to tell if they’re around by looking for signs such as the tell-tale slide marks they leave from sliding on their bellies on riverbanks or in the snow. They are often out at dawn and dusk but can be quite aloof and easily startled. Sit yourself far away with a good pair of binoculars and enjoy watching them frolic and play knowing that your local habitats are thriving.
In the West Kootenays they’ve been spotted in places like the Creston wetlands, and the Kootenay and Columbia Rivers near Nelson, Castlegar, and Trail.
Kathryn Martin and Marcus Archambault are second year Recreation, Fish and Wildlife students at Castlegar’s Selkirk College.
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